Magnetic disc drive storage devices store digital data on rotatable magnetizable disc surfaces. Data are written to and read from concentric tracks on the disc by read and write transducers, usually called “heads”, that are supported by an actuator arm that positions the head relative to the tracks on the confronting disc. A voice-coil actuator motor rotates the actuator arm to move the head along an arcuate path generally radially across the disc. Actuator current applied to the actuator motor accelerates the rotational motion of the arm to move the head radially across the disc.
The head reads position data identifying its position on the disc and supplies position data to a seek controller. The seek controller is responsive to the position data to operate in either of two modes, a track seek mode or a track follow mode. In the track follow mode, the seek controller supplies a small current to the actuator motor to move the arm and maintain the head over the center of the selected track being followed.
In the track seek mode, the seek controller supplies current to the actuator motor to accelerate and decelerate movement of the arm across several radial tracks between an initial or start track and a desired destination track. Many disc drive seek controllers employ sets of velocity profiles in the form of lookup tables that identify reference or demand velocities over the acceleration and deceleration phases of the seek. A velocity profile is selected based on the start and destination tracks of the seek operation. The controller applies a current to the actuator motor as selected from the table to accelerate radial movement of the head until the actual velocity equals a peak demand velocity of the selected seek profile. Ordinarily, the demand velocity varies as a function of the seek distance-to-go so that the controller accelerates the actuator to the peak demand velocity and then decelerates the actuator to near zero at the destination track.
In long seeks, the peak demand velocity might match a design maximum velocity of the disc drive, in which case the velocity profile includes a “coast” phase between the acceleration and deceleration phases where the demand velocity is constant and is equal to the design maximum velocity for the disc drive. Upon reaching the destination track, the seek controller switches from the seek mode to the track follow mode.
The controller employs a closed loop control that attempts to minimize the velocity error between the actual velocity and the demand velocity. At the beginning of a seek operation, the demand velocity ordinarily is a high value due to the large distance-to-go seek length. Usually, the demand velocity is equal to the peak demand velocity of the selected velocity profile at the start of the seek and over the acceleration phase. Because the actual velocity of the actuator is at or near zero at the start of a seek and the demand velocity is at its peak, there is a large initial velocity error. The closed loop nature of the seek controller will attempt to reduce the velocity error as quickly as possible. Consequently, the controller accelerates the actuator by forcing a maximum current into the actuator motor. The high current induces considerable noise and vibration in the disc drive. During the coast and deceleration phases, the actual velocity closely matches the demand velocity, so the current is acoustically quiet.
The velocity lookup tables are used by the seek controller to supply current to the actuator motor and control the actuator velocity radially across the disc. The controller pumps current into the actuator voice coil motor to accelerate the actuator until the actual velocity reaches the peak demand velocity required by the lookup table. The controller thereafter operates the actuator motor to decelerate the actuator from the peak demand velocity to zero at the destination track. In long seeks, the peak demand velocity may be the design maximum velocity established for the disc drive, in which case the acceleration phase ends at the maximum velocity and the deceleration phase begins at the maximum velocity. In any case, during the deceleration phase, and any coast phase, the velocity error is small so the closed loop controller will closely “follow” the demand velocity profile until the final destination track is reached.
Employing a single lookup table from seek start to seek end is a simple approach, but acoustically noisy. To reduce noise and vibration during seek operations, Seagate Technology LLC introduced the use of two lookup tables for each seek operation into certain of its Cheetah® disc drives. One table is based on a position-velocity profile over a normalized acceleration phase of the seek. The other table is selected from a group of deceleration phase position-velocity tables. Two scaling factors, called Vscale and Xscale factors, are used to manipulate the demand velocity profile of the acceleration lookup table. The peak demand velocity (end velocity) of the manipulated acceleration lookup table is intended to closely match the peak demand velocity (starting velocity) of the deceleration lookup table to complete the seek cycle. The Vscale and Xscale factors are derived from the seek length associated with the seek command and the design maximum velocity for the disc drive seek.
The technique employed in the Cheetah disc drive works quite well, especially on long seeks where the actuator arm is permitted to “coast” at the design maximum velocity between the acceleration and deceleration phases. However on shorter seeks, there is no “coast” phase between the acceleration and deceleration phases. Consequently, if the peak demand velocity of the manipulated acceleration table did not exactly match the peak demand velocity of the selected deceleration table, an abrupt change in demand velocity occurred at the cross-over from the acceleration to the deceleration phase. This change in demand velocity resulted in a mis-match of the peak velocities of the acceleration and deceleration phases, occasionally generating a noticeable noise that adversely affected operation of the disc drive.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.